The present invention generally relates to facsimile communication systems, and more particularly to a facsimile communication system which reduces the communication time by reducing the protocol.
In a conventional facsimile communication system, a facsimile communication is made in conformance with a transmission control procedure which is standardized by the CCITT Recommendations T.30 as a document facsimile transmission procedure for a general telephone switching network.
In other words, after a sequence of making a call set-up and capturing a line is made between a transmitting station and a receiving station, the transmitting station confirms the capability of the receiving station such as the transmission speed and the document size. The transmitting station transmits an image signal related to a document which is to be transmitted after checking the transmission speed which can be used for the communication on the connected line.
An example of the protocol between the transmitting and receiving stations will now be described with reference to FIG. 1. When the transmitting station dials to the receiving station and the receiving station is called, the receiving station transmits a called station identification (CED) signal having a frequency of 2100 Hz. After the CED signal ends, the receiving station transmits a digital identification (DIS) signal or a non-standard facilities (NSF) signal depending on whether the receiving station has the function of receiving in conformance with the CCITT standards or a specific function in conformance with a procedure other than the T-series CCITT Recommendations.
On the other hand, the transmitting station designates a function from the functions indicated by the DIS or NSF signal by transmitting a digital command (DCS) signal or a non-standard set-up (NSS) signal to the receiving station. After transmitting the CDS signal, the transmitting station transmits a training check (TCF) signal after a pause time which is provided to switch to a high-speed modem.
When the adjustment of the high-speed modem is completed by this training sequence, the receiving station transmits a confirmation to receive (CFR) signal and seeks transmission of the message from the transmitting station.
Therefore, a negotiation protocol (that is, phase B) of the facsimile communication is completed and the transmitting station transmits an image (PIX) signal. According to this conventional system, however, there is a problem in that it takes at least approximately 9.0 to 13.0 seconds for the negotiation protocol before the PIX signal is actually transmitted, as may be seen from FIG. 1.
However, the information quantity to be transmitted by the facsimile communication is increasing and the facsimile communication between distant stations is made more frequently due to the convenience of facsimile machines. For this reason, there are demands to reduce the communication time of the facsimile communication.